Pipe junction restrainers and techniques for their assembly have been developed to make fluid-tight connections between two axially-aligned pipes, joints, valves, fittings, hydrants, or other types of fluid connections. Often, these junction restrainers must withstand extraordinarily great pressures and tensile loads associated with water distribution and sewer connections.
It has been a current trend to employ polyvinyl chloride (PVC) plastic pipe in new construction. PVC pipes are often connected by a solvent weld or threaded joint. Solvent cement joints, while popular, release volatile gas and vapors which are unhealthy to workers and the environment. Glued joints also require substantial destruction of the coupling and piping in order to disassemble them. Threaded joints have been widely used on smaller pipe diameters in bell and spigot and same-diameter coupling designs. While threaded joints can be unscrewed, the task is usually time consuming and increases labor costs, especially if a PTFE tape or other sealant is used. Pipe-thread type joints are also easily distorted and damaged during pipe installation.
Newer systems have included a flexible spline as a restraining device. One popular system employed for connecting PVC pipe, sold under the trademark CERTA-LOK.TM. and produced by CertainTeed Corporation, Valley Forge, Pennsylvania, provides a restrained joint between a pair of pipe sections for municipal, fire protection, mining, irrigation, well casings, and other industrial uses. The CERTA-LOKT.TM. system forms a restraining mechanical lock that has a rating of about 150 psi and up. Since the restraining mechanism of the CERTA-LOK.TM. joint connector is uniformly distributed around the PVC pipes, the risk of damaging the plastic sidewalls by localized stress can be minimized. Similar connector designs are disclosed in French Pat. No. 1,397,378.
More specifically, the CERTA-LOK.TM. system provides a bell and spigot-type pipe connection for making a fluid connection between first and second pipes. This connection includes a first pipe having a first end, including a generally bell-shaped inner surface including a first annular recess or groove, and a second pipe having a second end sized to fit within a cavity defined by the generally bell-shaped inner surface of the first pipe. The second pipe includes a second annular recess or groove which can be aligned with the first annular recess of the bell-shaped inner surface of the first pipe to establish an annular cavity. The connection further includes an access hole disposed through a sidewall of the first end of the first pipe and communicating with the annular cavity. The flexible spline is inserted through this access hole and into the annular cavity for providing reversible restraint to the connection. Prior to insertion of the second pipe into the first pipe, an elastomeric fluid gasket is disposed between the bell-shaped inner surface of the first pipe and the outer surface of the second pipe, distally from the annular cavity, to provide a fluid-tight seal between the first and second pipes.
Bell and spigot type connections such as the CERTA-LOK.TM. system are lightweight and easy to handle, corrosion-resistant and easily reversible. Since no solvent cements are required, these connections are environmentally friendly and the connection joint achieves full strength immediately in all weather conditions. Bell and spigot-type connections also require no separate flanges, sleeves or tubular couplings.
Precise alignment and depth of the spline-receiving grooves of the first end second pipes of a bell and spigot pipe connection are essential for ensuring a proper connection between the pipe sections. If the grooves are slightly misaligned or if one or both of the grooves is of insufficient depth, the annular cavity formed thereby may be sufficiently occluded to hinder or perhaps prevent insertion of the spline into the cavity.
Because of the physical limitations of any plastic pipe fabrication process, virtually all plastic pipes are inherently lightly oblate or "out-of round". Moreover, the bell portions of such pipes vary considerably in wall thickness and diameter depending on the intended service application of the pipe.
These factors, as well as pipe length, render precise groove formation rather difficult. Consequently, existing machinery for groove cutting such as lathes, routers, and the like, which are suitable for cutting grooves in short length and virtually round pipes, have limited utility if used to form grooves of precise axial position and uniform depth in the internal wall surfaces of the bell portions of elongated plastic pipes.
An advantage exists, therefore, for an apparatus which is capable of forming annular grooves of precise position and depth in the interior wall of the bell portions of plastic pipes of varying sizes with minimal machinery adjustment being required as cut pipe is replaced in the machine by an uncut pipe.